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Atomically thin half-van der Waals metals enabled by confinement heteroepitaxy

Abstract

Atomically thin two-dimensional (2D) metals may be key ingredients in next-generation quantum and optoelectronic devices. However, 2D metals must be stabilized against environmental degradation and integrated into heterostructure devices at the wafer scale. The high-energy interface between silicon carbide and epitaxial graphene provides an intriguing framework for stabilizing a diverse range of 2D metals. Here we demonstrate large-area, environmentally stable, single-crystal 2D gallium, indium and tin that are stabilized at the interface of epitaxial graphene and silicon carbide. The 2D metals are covalently bonded to SiC below but present a non-bonded interface to the graphene overlayer; that is, they are ‘half van der Waals’ metals with strong internal gradients in bonding character. These non-centrosymmetric 2D metals offer compelling opportunities for superconducting devices, topological phenomena and advanced optoelectronic properties. For example, the reported 2D Ga is a superconductor that combines six strongly coupled Ga-derived electron pockets with a large nearly free-electron Fermi surface that closely approaches the Dirac points of the graphene overlayer.

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Fig. 1: CHet with defect-engineered epitaxial graphene.
Fig. 2: Atomic structure of CHet-grown 2D metals.
Fig. 3: Electronic structure of CHet-grown 2D Ga.
Fig. 4: Superconductivity in 2D Ga grown via CHet.
Fig. 5: Theoretical calculations on heterostructures of graphene and 2D Ga.

Data availability

The data that support the findings of this study are available at 10.6084/m9.figshare.c.4830711 or from the authors on reasonable request. See author contributions for specific data sets.

Code availability

Code used for computational investigations presented in this manuscript is available at gitlab.com/QEF/q-e/tree/qe-6.3 (EPW v5.0.0, Quantum Espresso v6.3) and www.vasp.at (VASP).

References

  1. 1.

    Rhodes, D., Chae, S. H., Ribeiro-Palau, R. & Hone, J. Disorder in van der Waals heterostructures of 2D materials. Nat. Mater. 18, 541–549 (2019).

    CAS  Article  Google Scholar 

  2. 2.

    Al Balushi, Z. Y. et al. Two-dimensional gallium nitride realized via graphene encapsulation. Nat. Mater. 15, 1166–1171 (2016).

    CAS  Article  Google Scholar 

  3. 3.

    Maniyara, R. A. et al. Tunable plasmons in ultrathin metal films. Nat. Photon. 13, 328–333 (2019).

    CAS  Article  Google Scholar 

  4. 4.

    Shah, D., Reddy, H., Kinsey, N., Shalaev, V. M. & Boltasseva, A. Optical properties of plasmonic ultrathin TiN films. Adv. Opt. Mater. 5, 1700065 (2017).

    Article  CAS  Google Scholar 

  5. 5.

    Riedl, C., Coletti, C. & Starke, U. Structural and electronic properties of epitaxial graphene on SiC (0001): A review of growth, characterization, transfer doping and hydrogen intercalation. J. Phys. D Appl. Phys. 43, 374009 (2010).

    Article  CAS  Google Scholar 

  6. 6.

    Emtsev, K. V., Zakharov, A. A., Coletti, C., Forti, S. & Starke, U. Ambipolar doping in quasifree epitaxial graphene on SiC (0001) controlled by Ge intercalation. Phys. Rev. B 84, 125423 (2011).

    Article  CAS  Google Scholar 

  7. 7.

    Gierz, I. et al. Electronic decoupling of an epitaxial graphene monolayer by gold intercalation. Phys. Rev. B 81, 235408 (2010).

    Article  CAS  Google Scholar 

  8. 8.

    Virojanadara, C., Watcharinyanon, S., Zakharov, A. A. & Johansson, L. I. Epitaxial graphene on 6H-SiC and Li intercalation. Phys. Rev. 82, 205402 (2010).

    Article  CAS  Google Scholar 

  9. 9.

    Subramanian, S. et al. Properties of synthetic epitaxial graphene/molybdenum disulfide lateral heterostructures. Carbon 125, 551–556 (2017).

    CAS  Article  Google Scholar 

  10. 10.

    Moulder, J. F. & Chastain, J. Handbook of X-ray Photoelectron Spectroscopy: a Reference Book of Standard Spectra for Identification and Interpretation of XPS Data (Perkin-Elmer, 1992).

  11. 11.

    Beamson, G. & Briggs, D. High Resolution XPS of Organic Polymers: the Scienta ESCA300 Database (Wiley, 1992).

  12. 12.

    Eckmann, A. et al. Probing the nature of defects in graphene by Raman spectroscopy. Nano Lett. 12, 3925–3930 (2012).

    CAS  Article  Google Scholar 

  13. 13.

    Vishwakarma, R. et al. Transfer free graphene growth on SiO2 substrate at 250 °C. Sci. Rep. 7, 43756 (2017).

    Article  Google Scholar 

  14. 14.

    Araby, M. I. et al. Graphene formation at 150 °C using indium as catalyst. RSC Adv. 7, 47353–47356 (2017).

    CAS  Article  Google Scholar 

  15. 15.

    Fujita, J. et al. Near room temperature chemical vapor deposition of graphene with diluted methane and molten gallium catalyst. Sci. Rep. 7, 12371 (2017).

    Article  CAS  Google Scholar 

  16. 16.

    Yi, C. et al. Evidence of plasmonic coupling in gallium nanoparticles/graphene/SiC. Small 8, 2721–2730 (2012).

    CAS  Article  Google Scholar 

  17. 17.

    Losurdo, M. et al. Demonstrating the capability of the high-performance plasmonic gallium-graphene couple. ACS Nano 8, 3031–3041 (2014).

    CAS  Article  Google Scholar 

  18. 18.

    Khorasaninejad, M. et al. Highly enhanced Raman scattering of graphene using plasmonic nano-structure. Sci. Rep. 3, 2936 (2013).

    CAS  Article  Google Scholar 

  19. 19.

    Voloshina, E., Rosciszewski, K. & Paulus, B. First-principles study of the connection between structure and electronic properties of gallium. Phys. Rev. B 79, 045113 (2009).

    Article  CAS  Google Scholar 

  20. 20.

    Ashcroft, N. W. & Mermin, N. D. Solid State Physics (Holt, Rinehart and Winston, 1976).

  21. 21.

    Yoshizawa, S., Kim, H., Hasegawa, Y. & Uchihashi, T. Disorder-induced suppression of superconductivity in the Si(111)-(7 × 3)-In surface: scanning tunneling microscopy study. Phys. Rev. B 92, 041410 (2015).

    Article  CAS  Google Scholar 

  22. 22.

    Yang, L., Deslippe, J., Park, C.-H., Cohen, M. L. & Louie, S. G. Excitonic effects on the optical response of graphene and bilayer graphene. Phys. Rev. Lett. 103, 186802 (2009).

    Article  CAS  Google Scholar 

  23. 23.

    Zhang, Y., Tan, Y.-W., Stormer, H. L. & Kim, P. Experimental observation of the quantum Hall effect and Berry’s phase in graphene. Nature 438, 201–204 (2005).

    CAS  Article  Google Scholar 

  24. 24.

    Popescu, V. & Zunger, A. Extracting E versus \(\overrightarrow{k}\) effective band structure from supercell calculations on alloys and impurities. Phys. Rev. B 85, 085201 (2012).

    Article  CAS  Google Scholar 

  25. 25.

    Gregory, W. D., Sheahen, T. P. & Cochran, J. F. Superconducting transition and critical field of pure gallium single crystals. Phys. Rev. 150, 315–321 (1966).

    CAS  Article  Google Scholar 

  26. 26.

    Chen, T. T., Chen, J. T., Leslie, J. D. & Smith, H. J. T. Phonon spectrum of superconducting amorphous bismuth and gallium by electron tunneling. Phys. Rev. Lett. 22, 526–530 (1969).

    CAS  Article  Google Scholar 

  27. 27.

    Wühl, H., Jackson, J. E. & Briscoe, C. V. Superconducting tunneling in the low-temperature phases of gallium. Phys. Rev. Lett. 20, 1496–1499 (1968).

    Article  Google Scholar 

  28. 28.

    Parr, H. & Feder, J. Superconductivity in β-phase gallium. Phys. Rev. B 7, 166–181 (1973).

    CAS  Article  Google Scholar 

  29. 29.

    Werthamer, N. R. Theory of the superconducting transition temperature and energy gap function of superposed metal films. Phys. Rev. 132, 2440–2445 (1963).

    Article  Google Scholar 

  30. 30.

    Reyren, N. et al. Superconducting interfaces between insulating oxides. Science 317, 1196–1199 (2007).

    CAS  Article  Google Scholar 

  31. 31.

    Oliveira, M. H. Jr, Schumann, T., Ramsteiner, M., Lopes, J. M. J. & Riechert, H. Influence of the silicon carbide surface morphology on the epitaxial graphene formation. Appl. Phys. Lett. 99, 111901 (2011).

    Article  CAS  Google Scholar 

  32. 32.

    Kruskopf, M. et al. A morphology study on the epitaxial growth of graphene and its buffer layer. Thin Solid Films 659, 7–15 (2018).

    CAS  Article  Google Scholar 

  33. 33.

    Kruskopf, M. et al. Comeback of epitaxial graphene for electronics: large-area growth of bilayer-free graphene on SiC. 2D Mater. 3, 041002 (2016).

    Article  CAS  Google Scholar 

  34. 34.

    Zhang, T. et al. Superconductivity in one-atomic-layer metal films grown on Si(111). Nat. Phys. 6, 104–108 (2010).

    CAS  Article  Google Scholar 

  35. 35.

    Margine, E. R. & Giustino, F. Anisotropic Migdal-Eliashberg theory using Wannier functions. Phys. Rev. B 87, 024505 (2013).

    Article  CAS  Google Scholar 

  36. 36.

    McMillan, W. L. Transition temperature of strong-coupled superconductors. Phys. Rev. 167, 331–344 (1968).

    CAS  Article  Google Scholar 

  37. 37.

    Allen, P. B. & Dynes, R. C. Transition temperature of strong-coupled superconductors reanalyzed. Phys. Rev. B 12, 905–922 (1975).

    CAS  Article  Google Scholar 

  38. 38.

    Garno, J. P. Simple high vacuum evaporation system with low-temperature substrate. Rev. Sci. Instrum. 49, 1218–1220 (1978).

    CAS  Article  Google Scholar 

  39. 39.

    Ludbrook, B. M. et al. Evidence for superconductivity in Li-decorated monolayer graphene. Proc. Natl Acad. Sci. USA 112, 11795–11799 (2015).

    CAS  Article  Google Scholar 

  40. 40.

    Ichinokura, S., Sugawara, K., Takayama, A., Takahashi, T. & Hasegawa, S. Superconducting calcium-intercalated bilayer graphene. ACS Nano 10, 2761–2765 (2016).

    CAS  Article  Google Scholar 

  41. 41.

    Cao, Y. et al. Unconventional superconductivity in magic-angle graphene superlattices. Nature 556, 43–50 (2018).

    CAS  Article  Google Scholar 

  42. 42.

    Fu, L. & Kane, C. L. Superconducting proximity effect and Majorana fermions at the surface of a topological insulator. Phys. Rev. Lett. 100, 096407 (2008).

    Article  CAS  Google Scholar 

  43. 43.

    Boltasseva, A. & Shalaev, V. M. Transdimensional photonics. ACS Photon. 6, 1–3 (2019).

    CAS  Article  Google Scholar 

  44. 44.

    Giannozzi, P. et al. QUANTUM ESPRESSO: a modular and open-source software project for quantum simulations of materials. J. Phys. Condens. Matter 21, 395502 (2009).

    Article  Google Scholar 

  45. 45.

    Kresse, G. & Joubert, D. From ultrasoft pseudopotentials to the projector augmented-wave method. Phys. Rev. B 59, 1758–1775 (1999).

    CAS  Article  Google Scholar 

  46. 46.

    Blöchl, P. E. Projector augmented-wave method. Phys. Rev. B 50, 17953–17979 (1994).

    Article  Google Scholar 

  47. 47.

    Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple. Phys. Rev. Lett. 77, 3865–3868 (1996).

    CAS  Article  Google Scholar 

  48. 48.

    Perdew, J. P., Burke, K. & Ernzerhof, M. Generalized gradient approximation made simple [Phys. Rev. Lett. 77, 3865 (1996)]. Phys. Rev. Lett. 78, 1396 (1997).

    CAS  Article  Google Scholar 

  49. 49.

    Marzari, M., Vanderbilt, D., De Vita, A. & Payne, M. C. Thermal contraction and disordering of the Al(110) surface. Phys. Rev. Lett. 82, 3296–3299 (1999).

    CAS  Article  Google Scholar 

  50. 50.

    Stukowski, A. Visualization and analysis of atomistic simulation data with OVITO–the open visualization tool. Model. Sim. Mater. Sci. Eng. 18, 015012 (2010).

    Article  Google Scholar 

  51. 51.

    Momma, K. & Izumi, F. VESTA 3 for three-dimensional visualization of crystal, volumetric and morphology data. J. Appl. Crystallogr. 44, 1272–1276 (2011).

    CAS  Article  Google Scholar 

  52. 52.

    Makov, G. & Payne, M. C. Periodic boundary conditions in calculations. Phys. Rev. B 51, 4014–4022 (1995).

    CAS  Article  Google Scholar 

  53. 53.

    Neugebauer, J. & Scheffler, M. Adsorbate-substrate and adsorbate-adsorbate interactions of Na and K adlayers on Al(111). Phys. Rev. B 46, 16067–16080 (1992).

    CAS  Article  Google Scholar 

  54. 54.

    Enkovaara, J. et al. Electronic structure calculations with GPAW: a real-space implementation of the projector augmented-wave method. J. Phys. Condens. Matter 22, 253202 (2010).

    CAS  Article  Google Scholar 

  55. 55.

    Kresse, G. & Furthmüller, J. Efficient iterative schemes for total-energy calculations using a plane-wave basis set. Phys. Rev. B 54, 11169–11186 (1996).

    CAS  Article  Google Scholar 

  56. 56.

    Heyd, J., Scuseria, G. E. & Ernzerhof, M. Hybrid functionals based on a screened Coulomb potential. J. Chem. Phys. 118, 8207–8215 (2003).

    CAS  Article  Google Scholar 

  57. 57.

    Hartwigsen, C., Goedecker, S. & Hutter, J. Relativistic separable dual-space Gaussian pseudopotentials from H to Rn. Phys. Rev. B 58, 3641–3662 (1998).

    CAS  Article  Google Scholar 

  58. 58.

    Noffsinger, J. et al. EPW: a program for calculating the electron–phonon coupling using maximally localized Wannier functions. Comp. Phys. Commun. 181, 2140–2148 (2010).

    CAS  Article  Google Scholar 

  59. 59.

    Giustino, F., Cohen, M. L. & Louie, S. G. Electron-phonon interaction using Wannier functions. Phys. Rev. B 76, 165108 (2007).

    Article  CAS  Google Scholar 

  60. 60.

    Souza, I., Marzari, N. & Vanderbilt, D. Maximally localized Wannier functions for entangled energy bands. Phys. Rev. B 65, 035109 (2001).

    Article  CAS  Google Scholar 

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Acknowledgements

Funding for this work was provided by the Northrop Grumman Mission Systems’ University Research Program, Semiconductor Research Corporation Intel/Global Research Collaboration Fellowship Program, task 2741.001, National Science Foundation (NSF) CAREER Awards 1453924 and 1847811, the Chinese Scholarship Council, an Alfred P. Sloan Research Fellowship, NSF DMR-1708972 and 1808900, and the 2D Crystal Consortium NSF Materials Innovation Platform under cooperative agreement DMR-1539916. A portion of this research was conducted at the Center for Nanophase Materials Sciences, which is a DOE Office of Science User Facility, and at the Pennsylvania State University Materials Research Institute’s Material Characterization Laboratory. This research used resources of the Advanced Light Source, which is a DOE Office of Science User Facility under contract no. DE-AC02-05CH11231. We acknowledge Haiying Wang for help with STEM sample cross-section preparation via FIB; Vince Bojan, Nabil Bassim and Heshem Elsherif for help with AES; and Max Wetherington for Raman spectroscopy support.

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N.B, B.B., Y.W., V.C. and J.A.R. wrote the paper with input from the co-authors. N.B. performed CHet and XPS characterization and assisted in the Raman spectroscopy and SEM characterization. B.B performed the Raman spectroscopy and SEM characterization and assisted in sample preparation and electrical characterization. Y.W. performed DFT modelling of graphene/Ga/SiC heterostructures in consultation with V.C. with input from J.Z., B.B., N.B. and J.A.R.; J.J. performed electrical measurements under the direction of C.Z.C. with input from B.B and J.Z.; R.K., A.B. and C.J. performed ARPES measurements under the direction of E.R.; N.N. performed graphene defect modelling under the direction of A.v.D.; and K.W. performed cross-sectional STEM imaging. M.K. and W.K. prepared the LEED instrument for EG/metal/SiC samples, and M.K. performed the LEED measurements. A.D.L.F.D. assisted with CHet and material characterization. C.D. and S.S. performed the EG synthesis under the direction of J.A.R.; J.S. assisted in XPS data analysis. M.F., Q.Z., G.Z. and A.P.L. performed the scanning probe characterization. Y.W.C. assisted with electrical measurements under the direction of J.Z.

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Correspondence to Joshua A. Robinson.

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Supplementary Figs. 1–22, note and Table 1

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Briggs, N., Bersch, B., Wang, Y. et al. Atomically thin half-van der Waals metals enabled by confinement heteroepitaxy. Nat. Mater. 19, 637–643 (2020). https://doi.org/10.1038/s41563-020-0631-x

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